The present invention relates in general to metal-to-metal seals, and in particular to an improved gasket for sealing between a wellhead housing and a wellhead connector.
In oil and gas wellhead assemblies, tubular members are connected end-to-endand sealed by a gasket or seal ring. One type of seal ring, particularly used in subsea wellhead assemblies, is of metal and has upper and lower legs. A rib extends radially outward from a junction of the legs. Each leg has a conical sealing surface that engages a conical seat on one of the wellhead members. The conical sealing surface is a continuous cone that extends from the tip of the leg to the rib. The taper angle of the sealing surface is typically slightly different that the taper angle of the seat, creating an interference metal-to-metal sealing engagement. A coating, such as a silver alloy, may be applied to the sealing surface to enhance sealing.
This type of seal works well. However, improvements are desired in the ability of the seal to seal against high pressure gas over long periods of time.
The seal of this invention has two oppositely extending legs and a rib extending radially from the junction of the legs. A pair of sealing bands are located on at least one of the legs. The sealing bands are separated by an annular recess. One of the sealing bands extends from the tip of the leg to the recess. The other extends from the rib to the recess.
Preferably, the bands are located in the same conical surface of revolution. The taper angle is slightly smaller relative to the axis of the seal ring, than the seat. This causes greater contact pressure in the sealing band located adjacent the tip than the one next to the rib. A coating of molybdenum sulfide is applied to the sealing bands in the preferred embodiment. The recess has tapered upper and lower edges, and in the preferred embodiment, has a concave base.
Preferably, both legs are identical. However, one version of the seal has a contingent seal leg in the event the conical seat on the lower tubular member is damaged. The contingent seal leg has only a single sealing band, and it is located adjacent the tip and separated by as support section. The contingent seal band is at a much steeper angle, relative to the axis of the seal ring, than the two seal bands on the opposite leg.